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TD-SCDMA Principle Part A: Basic Concept in Mobile Communication Dr. Shihe Li e-mail: lish@pub.tdscdma.com Datang MobileCo. Contents. Part A: Basic concept Review Multiplex CDMA Duplex Coverage. History of Mobile Communication. Early period: from early 50’s: Military application

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  1. TD-SCDMA PrinciplePart A: Basic Concept in Mobile CommunicationDr. Shihe Lie-mail: lish@pub.tdscdma.comDatang MobileCo

  2. Contents Part A: Basic concept • Review • Multiplex • CDMA • Duplex • Coverage

  3. History of Mobile Communication • Early period: from early 50’s: • Military application • Without system concept • Analog voice and signaling • Single BS operation • Concept of cellular in 70’s • Cellular concept • Frequency Reuse • The 1 G: Analog system in 80’s • Different standard in each country • The 2G: Digital system in 90’s • GSM/CDMA(IS-95) • Universal standard • Duplex is 1G/2G: FDD Cellular Concept

  4. Mobile Network ___1st generation OAM BS PSTN Mobile SW HS or MS

  5. Mobile Network ___2nd generation ACU OAM BS PSTN Mobile SW With data HS or MS PDN BSC

  6. Mobile Network ___3rd generation ACU OAM Node_B Mobile SW Circuit and Packet PSTN UE PDN RNC Internet

  7. CN and Radio Access • Network: • Slow progress, from 1G to 3G, circuit switch take the same technology • Need longer period to stable • Low revenue and high profit (3% of market in mobile, but high margin) • Radio Access: • Fast change technologies • Key issue in mobile system and user terminals • Main part in equipment market, mobile communications • IMT-2000 asked proposal for RTT • 3 main stream standards are 3 different Radio Transmission Technology

  8. Q&S BER requirement for different service in different environment Spectrum efficiency Quantities of services provided in unit bandwidth Complexity – cost E&M compatibility Interference to other system Reject interference from other systems Contents of Physical layer Multiple access technology Duplexing Frame structure Data multiplexing Modulation Channel coding/Interleaving Signal detection Antenna technologies Random access Cell search Handover Other key technologies Basic Requirement for RTT

  9. One Generation per 10 years Widely application Standard 4G？ Product Development R/D 3G(CDMA) 2G(TDMA) 1G (FDMA) 70 80 90 00 10

  10. Contents Part A • Review • Multiplex • CDMA • Duplex • Coverage

  11. What is Multiplex means • Multiple users share a same frequency band • Possible way for multiple access • Frequency Division Multiple Access (FDMA) • Separating user by different carrier frequency • Most popular way to be used in all mobile system • Time Division Multiple Access (TDMA) • Separating user by different time slot in same carrier frequency • Common used in digital system • Code Division Multiple Access (CDMA) • Separating user by different code in same time and carrier frequency • Wide adopted in 3G technology • Space Division Multiple Access (SDMA) • Separating user by different location (direction) in same time, code, and carrier frequency • Future technology based on smart antenna

  12. Technology: 1G (TACS) • Cellular concept • BW for each carrier: 25kHz • 11 Group of carrier frequency • Basic Physical Layer Tech • Multiplex: FDMA • Analog modulation (FM) • Digital signaling • Basic Network concept • Circuit switch • Hard Handover A pair of ch., 25kHz BW each 890 915 935 960MHz HS Tx BS Tx

  13. Technology: 2G (GSM) A pair of ch., 200kHz BW each (8 TACS ch) • Cellular concept • BW for each carrier: 200kHz • 7 Group of carrier frequency • Basic Physical Layer Tech • Multiplex: FDMA+TDMA • 8 time slots per carrier • Digital modulation • Digital signaling (improved) • Basic Network concept • Circuit switch • Hard Handover • International roaming • 9.6kbps data • 2.5G: GPRS/Edge 890 915 935 960MHz HS Tx BS Tx t f

  14. Technology: 2G/3G (CDMA FDD) A pair of ch., 1.25/5MHz BW each • Cellular concept • BW for each carrier: 1,228.8/3,840kHz • Same carrier frequency in adjacent cell • Basic Physical Layer Tech • Multiplex: FDMA+CDMA • Multiple codes per carrier • Digital modulation (QPSK) • Digital signaling (improved) • Basic Network concept • Circuit/Package switch • Hard and Soft Handover • International roaming • Voice(2G), Multimedia(3G) BS Tx HS Tx f

  15. Technology: TD-SCDMA A pair of ch., 1,600kHz BW each • Cellular concept • BW for each carrier: 1,600kHz • Same carrier frequency in adjacent cell • Basic Physical Layer Tech • Multiplex: FDMA+TDMA+CDMA • 16 codes per TS per carrier • Digital modulation (QPSK) • Digital signaling (improved) • Basic Network concept • Circuit/Package switch • Hard and Boton Handover • International roaming • Multimedia t f

  16. Frequency Plan • Both FDMA and TDMA need frequency plan__Interference in adjacent carrier • Frequency re-use factor • FDMA: same carrier shall be separated by two cells: re-use factor = 11 • TDMA: same carrier shall be separated by one cells: re-use factor = 7 • CDMA: Adjacent cell can use same carrier, re-use factor = 1

  17. Spectrum Efficiency for voice services in 1/2G systems • 1G FDMA(TACS) • 2 x 25kHz for 1 voice ch., frequency re-use factor=11 • Spectrum efficiency=1/0.05/11=1.8ch/cell/MHz • 2G TDMA(GSM) • 2 x 200kHz for 8 voice ch., frequency re-use factor=7 • Spectrum efficiency=8/0.4/7=2.8ch/cell/MHz • 2G CDMA(IS-95) • 2 x 1.25MHz for 20 voice ch., frequency re-use factor=1 • Spectrum efficiency=20/2.5/1=8ch/cell/MHz • Theoretically, if all code can be used, the spectrum efficiency may reach 64/2.5/1=25.8ch/cell/MHz, which is nearly 14 times of FDMA and 8 times of TDMA.

  18. Contents Part A • Review • Multiplex • CDMA • Duplex • Coverage

  19. Basic CDMA concept • Spectrum Spreading is a technology used in military communication since 60’s • Basic concept • Spreading code: Walsh code, it is an orthogonal code when synchronized • CDMA is a self-interference system: • Multiplex interference: between code channels • Multi-path and Doppler • Interference from other system and users in adjacent cell • Near-far effect • Capacity of a CDMA system is limited by total interference level

  20. Basic CDMA IS-95 concept • IS-95 is a FDD CDMA system • Operated in AMPS frequency band (taking BW of 41 AMPS carriers) • Chiprate 1.2288Mcps • Carrier separation 1.23MHz • Channel code and interleaving • Spreading factor: 64 • Studying in late 80’ for public mobile communication, the mainly contributions by Qualcomm are as follows • Two sets of code: short code (Walsh) for distinguish user in the cell and long code (PN code) for distinguish cell • Strict up-link power control: to overcome near-far effect • Receiver: Rake receiver to overcome multi-path • Macro-diversity and soft-handover: to enhance capacity and handover without interrupt (suitable for data transmission) • Variable rate voice coder to enhance capacity

  21. Capacity in CDMA system: General situation • Basic consumption: • Ideal power control, received power level from each active UE is the same: Eb • User distribution: uniform • When N users are active, then the interference from the same cell will be (N-1)Eb. The total interference from the adjacent cells (1st and 2nd layers) will be the same as that from the same cell. • double Eb/N0≤lg(SF)+Eb/(N0+2*(N-1)Eb)~ lg(SF)-lg(2N) N≤(10lg(SF)-Eb/N0)/2 • Reduce interference

  22. Technologies related to capacity • Macro diversity • UE get down-link from 2 to 3 BSs • Each BS may transmit less power, less interference to enhance down-link capacity about 2 dB • Power control • Power control error: usually 2 to 3 dB • Because of fast fading and multi-path • Capacity loss: 2dB

  23. The possible way to improve CDMA system • Variable code rate (by Qualcom in IS-95) • Based on voice performance, reduce coding rate. • May double capacity (half interference) for CDMA • Key IPR for Qualcom • Useless in Data service • Smart Antenna (by TD-SCDMA) • Most efficient tech • Capacity enhance by N times (N is the number of antenna elements) • Coding tech: zero-interference window (by LAS-CDMA) • Limited number of code when need wider ZIW • Can be used in high speed data link only (number of user very low at the same time)

  24. Contents Part A • Review • Multiplex • CDMA • Duplex • Coverage

  25. Basic concept of Duplex F Fdown Fup • Duplex: communication between UE and BS simultaneously • Traditional tech: divided by frequency: FDD • Time Division Duplex (TDD) is from data communication • From end of 80’s, TDD started to use in voice communication (CT2, DECT, etc.) • From 3G, TDD become one duplex in RTT t Down link data Up link data TSdown TSup t

  26. Comparison between FDD & TDD

  27. Main Feature in TDD Duplex • Spectrum flexibility: do not need paired frequency • Same carrier frequency in both Down- and Up-link, symmetric propagation performance suitable for smart antenna, pre-Rake, open loop power control and other technologies • Support asymmetric data services, by adjusting different numbers of slots in up- and/or down-link • It may use of different bandwidth for asymmetric services in FDD, but it could not be flexible • Low cost: Do not ask high isolation between Tx and Rx path, one may design single IC for RF transceiver in UE

  28. Main Shortage for TDD • Higher peak/average tx power ratio for UE • FDD: continuous transmit • TDD: only one TS work, the extra ratio will be 10lgM, M is the number of TS • Higher requirement for transmitter and PA. • Lower sensitivity for receiver • Bandwidth: the total chiprate • Data rate: limited by number of TS • Sensitivity loss: 10lgM. • Discontinue operation • Less communication distance, half nearly • Difficult for high speed moving. t

  29. How to overcome the shortages? • The shortage of TDD leads to: • TDD can only be used in Micro- and Pico-cell • TDD can only support slow moving • Possible way to overcome the shortages • Smart antenna: increase sensitivity and EPRI • Smart antenna plus Joint detection: improve performance in fast fading (multi-path in high speed moving)

  30. Contents Part A • Review • Multiplex • CDMA • Duplex • Coverage

  31. How to calculate PR=PTmax-LTcable+GTA-Loss-Margin+GRA-LRcable • Margin: for slow fading and shadow, depends to environment, 11 to 15dB • Loss: depends to environment • Indoor (pico-cell) • Pedestrian (micro-cell) • Vehicular (macro-cell) • PR/(N+I) should be large than required Eb/N0, • N: depends to bandwidth and spread factor Tx Ant Path loss Tx & Rx Feed cable Rx Ant UE BS distance

  32. Wave Propagation Loss Indoor n=1 n=2 n=3 Loos (dB) 100 110 120 130 140 150 160 170 180 Pedestrian Vehicular 2GHz 900MHz ITU Model • Indoor: L= 30lgd + 54.35 (n=1) 30lgd + 70.52 (n=2) 30lgd + 80.59 (n=3) dB where n is the number of floors d is the distance in meter • Pedestrian: L=40lgd +30lgf + 49 =40lgd + 148dB • Vehicular: L= 40(1-0.004h)lgd- 18lgh +21lgf +80 =35.2lgd+122.7dB where f is frequency in MHz (2GHz); h is the hight of BS antenna over average roof level in meter(30m); d is the distance in kilometer. D=1 3 10 30 100 300 1k 3k 10km

  33. Example • For voice service, the required Eb/(N+I) will be 3.1dB when coding of R=1/3 is used. • Up-link, Ptx=21dBm for UE; antenna gain is 17dBi for BS and 0dBi for UE; cable loss is 2dB for BS and 0dB for UE. • For WCDMA, spreading factor=128 for 12.2kbps services. • Noise figure of 5dB for BS, then N0= -165+10lg(3.84M) = -99dBm • Then the required minimum receiving level: Pmin=-99-10lg(SF)+3.1= -117dBm • PR = PTmax-LTcable+GTA-Loss-Margin+GRA-LRcable= 21-0+0-Loss-Margin+17-2 =36-Loss-Margin≥-117 • In vehicular environment, margin takes 11dB, then Loss =146dB or 122.7+35.2lgd = 142, d = 10(19.3/35.2)=100.548 = 3.5km

  34. Cell Size • Link budget can not represent the possible cell size for CDMA system: one UE only, without interference from other UE • Maximum cell size shall be less than the maximum distance in a full loaded system • For a full loaded CDMA system, the total interference will be Itotal = (N-1)P0 which will much higher than white noise level. And the operation receiving level is 6dB higher than the sensibility. • As an example, P0 will be -111dBm for WCDMA for voice services. • PR = PTmax-LTcable+GTA-Loss-Margin+GRA-LRcable= 21-0+0-Loss-Margin+17-2 =36-Loss-Margin≥-111 • In vehicular environment, margin takes 11dB, then Loss =140dB or 118.7+35.2lgd = 140, d = 10(13.3/35.2)=100.378 = 2.5km

  35. Comm. Distance vs cell radius • In practical network, it should be cellular structure and multi-user operation; • The calculated and demonstrated communication distance may much larger than practical cell radius (double or more)

  36. Continue Part B: Basic Concept of TD-SCDMA • CDMA Review • Basic concept: Smart antenna • Basic concept: Synchronous CDMA • Basic concept: Software radio and SDR • System consideration

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